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Related Concept Videos

Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene π orbitals.
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)

Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
The extent of coupling depends on the C‑C bond length, the two H‑C‑C angles, any electron-withdrawing substituents, and the dihedral angle between the involved orbitals. The...
Propagation Speed of Electromagnetic Waves01:30

Propagation Speed of Electromagnetic Waves

Electromagnetic waves are consistent with Ampere's law. Assuming there is no conduction current Ampere's law is given as:
Susceptibility, Permittivity and Dielectric Constant01:26

Susceptibility, Permittivity and Dielectric Constant

When placed in an external electric field, a dielectric material gets polarized. The charge density in the dielectric material is given by the sum of the bound and free charge densities, while the total charge density can also be written in terms of the total electric field. The bound charge density can be measured in terms of polarization, leading to the relationship between electric displacement and polarization.
Debye–Huckel–Onsager Conductance Equation01:28

Debye–Huckel–Onsager Conductance Equation

The Debye-Hückel-Onsager equation is a cornerstone of physical chemistry, providing a method to determine the molar conductance (Λm) and molar conductance at infinite dilution (Λ°m) for uni-univalent electrolytes.Uni-univalent electrolytes are electrolytes that dissociate in solution to produce one cation with a +1 charge and one anion with a –1 charge per formula unit.This equation addresses two crucial phenomena: the asymmetry effect and the electrophoretic effect. According to this equation,...

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Related Experiment Video

Updated: Jun 15, 2026

Design and Fabrication of an Optical Fiber Made of Water
08:06

Design and Fabrication of an Optical Fiber Made of Water

Published on: November 8, 2018

Mode coupling coefficient measurements in optical fibers.

K Kitayama, M Ikeda

    Applied Optics
    |March 9, 2010
    PubMed
    Summary

    A new method measures mode coupling coefficients in multimode fibers using pulse waveforms. Strong coupling was observed in lower-order modes of nylon-sheathed fibers, likely due to microbends.

    Area of Science:

    • Optical Fiber Communications
    • Waveguide Theory

    Background:

    • Mode coupling in multimode fibers affects signal integrity.
    • Characterizing mode coupling is crucial for fiber optic performance.

    Purpose of the Study:

    • To develop and apply a method for measuring mode coupling coefficients in multimode fibers.
    • To investigate the relationship between fiber sheathing and mode coupling.

    Main Methods:

    • Developed a measurement technique for mode coupling coefficients.
    • Analyzed mode group pulse waveforms.
    • Conducted measurements on long and short multimode step-index fibers.

    Main Results:

    • Successfully calculated mode coupling coefficients from pulse waveforms.

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  • Observed strong mode coupling in lower-order modes for nylon-sheathed fibers.
  • Estimated microbending parameters: correlation length (2.0 mm) and standard deviation of curvature (4.2 x 10^-4 mm^-1).

    • Conclusions:

    • The developed method is effective for quantifying mode coupling in multimode fibers.
    • Nylon sheathing induces significant mode coupling, primarily in lower-order modes.
    • Microbending is a likely cause of the observed mode coupling.